Optical recording medium driving device

ABSTRACT

A method and an apparatus for driving an optical recording medium for recording and/or reproducing various information for the optical recording medium, in which the output power ratio of the light source may be reduced for recording and reproduction, for optical recording media of different sorts, or for respective recording surfaces of a multi-layered optical recording medium, so that optimum characteristics may be realized even with use of an easy-to-fabricate light source or a light source with a smaller light output rating. The intensity of a light beam emitted on an optical recording medium  102  by an optical head  104  is controlled by optical coupling efficiency varying elements  214, 215  depending on the sort of the optical recording medium  102 , recording surfaces of a multi-layered optical recording medium, recording surfaces in the multi-layered optical recording medium or on the operating modes, in such a manner that the intensity of the light beam emitted on the optical recording medium  102  may be significantly varied without drastically increasing the output power ratio on the side light source  212.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and an apparatus for driving anoptical recording medium for recording and/or reproducing variousinformation for the optical recording medium. This application claimspriority of Japanese Patent Application No. 2001-370497, filed on Dec.4, 2001, the entirety of which is incorporated by reference herein.

2. Description of Related Art

Among optical recording media, typified by optical discs, a disc havingpre-formed pits and used exclusively for replay, a disc which may berecorded and reproduced based on phase changes along a grooved structureor with the use of magneto-optical recording, and so forth, have so farbeen proposed. In the case of an optical recording medium drivingdevice, such as an optical disc device employing an optical disc, whichallows for recording and reproduction, a semiconductor laser, having alarger value of the maximum radiating light volume (maximum light outputrating) is customarily used as a light source for an optical head.Meanwhile, a light source of a larger value of the maximum rating isusually not necessary for the following reason:

-   (1) When a semiconductor laser has a low output, stabilized    oscillations can hardly be achieved, as a general rule, thus    increasing the laser noise. Thus, in order to achieve the CNR    (carrier to noise ratio) in reproducing the information, the laser    light output needs to be set to a more or less large value which    usually is 2 mW to 5 mW.-   (2) In the case of a recordable optical recording medium, the    information recording is by raising for example the temperature of    the recording layer by a light beam converged on a recording surface    thereof. In this case, if the two conditions of [no deterioration in    recording signals with the reproducing optical power] and [stable    recording with the recording optical power] are to be met, an output    ratio of the optical power in recording to that in reproduction    needs to be higher than a preset value. The maximum power of the    recording light is routinely 5 to 20 times that for the reproducing    light. In information recording at a rate higher than the standard    rate, a higher output ratio is required.

For the above reasons, the maximum light output rating for a lightsource used for an optical head for recording and reproduction and for alight source used for an optical head for recording and/or reproducingplural sorts of the optical recording medium is usually 20 mW to 50 mW.For an optical recording medium for information recording at a higherrate of the order of eight times the standard rate, such as an opticaldisc of the so-called CD-R/RW format, the same rating is of the order of100 mW.

However, the light source with a high maximum light output rating isdifficult to fabricate, while power consumption of the light source isundesirably increased. If, in this consideration, a smaller value of themaximum light output rating is to be used, the laser noise at the timeof reproduction is increased, such that replay characteristics achievedmay not be optimum.

In replay-only DVD, such as DVD-ROM or DVD-Video, both being registeredtrademarks, an optical disc having two recording surfaces has alreadybeen put to practical utilization. For optical discs which arerecordable and reproducible, proposals have already been made formulti-layered optical discs, having a multi-layered recording surface,such as two-layered or four-layered optical discs.

For these multi-layered optical recording media, the recording opticalpower and the reproducing optical power which are approximately 1.5 to 2times as large as or even higher than that for the optical recordingmedium having a sole recording surface is needed. Thus, in a systemadapted for coping with both an optical recording medium having a solerecording surface and an optical recording medium having pluralrecording surfaces, the ratio (multiplication factor) of the maximumrecording optical power for a multi-layered optical disc to thereproducing optical power for a single layer optical disc, on simpleapproximation, amounts to two or thereabouts.

Moreover, the required recording optical power or reproducing opticalpower differs in case of a differing linear velocity of the opticalrecording medium relative to the light beam. That is, if the linearvelocity of the optical recording medium relative to the light beam isincreased, a larger recording optical power and a larger reproducingoptical power are required.

Thus, with an increasing recording capacity, estimated in time to come,it may be premeditated that the dynamic range of the optical output ofthe light source has to be increased further.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a drivingdevice for an optical recording medium in which the laser noise inreproduction may sufficiently be reduced even with plural sorts of theoptical recording medium, such as plural sorts of the optical recordingmedium having different values of the optimum recording and/orreproducing optical power, a multi-layered optical recording medium, orwith an optical recording medium, the recording surface of which issplit into plural regions, and in which optimum recording and/orreproducing characteristics may be achieved for different sorts of theoptical recording medium, respective recording surfaces of themulti-layered optical recording medium or plural recording areas of asingle recording surface of the optical recording medium, even with useof a light source which may be fabricated readily inexpensively or alight source with a smaller value of the maximum optical output rating.

In one aspect, the present invention provides an optical recordingmedium driving device for recording and/or reproducing signals for atleast two sorts of optical recording media having respective differentvalues of the recording and/or reproducing power, in which the drivingdevice includes an optical head for emitting a light beam on the opticalrecording medium, optical coupling efficiency varying means for varyingthe optical coupling efficiency which is the ratio of the light volumeof a light beam condensed on the optical recording medium to the lightvolume of a light beam emitted by the optical head, and optical couplingefficiency controlling means for controlling the optical couplingefficiency varying means for varying the optical coupling efficiency.The optical coupling efficiency controlling means controls the opticalcoupling efficiency varying means depending on the sort of the opticalrecording media.

In another aspect, the present invention provides a driving method foran optical recording medium for recording and/or reproducing signals forat least two sorts of optical recording media having respectivedifferent values of the recording and/or reproducing power, in which thedriving method includes varying the optical coupling efficiency, whichis the ratio of the light volume of a light beam condensed on theoptical recording medium to the light volume of a light beam emitted bythe optical head adapted for emitting the light beam on the opticalrecording medium, by optical coupling efficiency varying means,depending on the sort of the optical recording medium.

With the optical recording medium driving device and method, accordingto the present invention, the optical coupling efficiency varying meansis controlled responsive to the sort of the optical recording medium asverified by the medium sort discriminating means, to the recordingsurface of the optical recording medium, as verified by the recordingsurface discriminating means or to the recording region of the recordingsurface of the optical recording medium, as verified by the recordingregion discriminating means, to provide for an optimum recording and/orreproducing optical power on the recording surface of the opticalrecording medium.

That is, with the optical recording medium driving device according tothe present invention, the laser noise in reproduction may besufficiently reduced for plural sorts of the optical recording medium,for multi-layered optical recording media or an optical recording mediumthe recording surface of which is divided into plural recording regions,such that, if a readily producible light source or a light source with asmaller value of the maximum optical output rating is used, therecording and/or reproducing characteristics achieved may be optimizedfor each of plural sorts of the optical recording medium, each recordingsurface of the multi-layered optical recording medium or each ofrespective recording regions of a recording surface of the opticalrecording medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a structure of an optical recordingmedium driving device, having an optical coupling efficiency varyingdevice and an optical head incorporated therein, according to anembodiment of the present invention.

FIG. 2 shows the structure of an optical head in an optical recordingmedium driving device.

FIG. 3 is a side view showing a portion of a recording and/orreproducing system of the optical recording medium driving device.

FIG. 4 is a graph showing the relationship between the “recommendedreproducing optical power” and a “recommended recording optical power”for an optical recording medium used in the optical recording mediumdriving device.

FIG. 5 is a side view showing a modification of a portion of therecording and/or reproducing system of the optical recording mediumdriving device.

FIGS. 6A and 6B are schematic views showing a first embodiment of afirst implementation system of an optical coupling efficiency varyingelement of an optical head in the optical recording medium drivingdevice.

FIGS. 7A and 7B are schematic views showing a second embodiment of thefirst implementation system of the optical coupling efficiency varyingelement of the optical head.

FIGS. 8A, 8B and 8C are schematic views showing a first embodiment of asecond implementation system of the optical coupling efficiency varyingelement of the optical head.

FIGS. 9A and 9B are schematic views showing a second embodiment of thesecond implementation system of the optical coupling efficiency varyingelement of the optical head.

FIGS. 10A and 10B are schematic views showing a structure of a liquidcrystal element as an optical coupling efficiency element shown in FIG.9.

FIGS. 10C and 10D are graphs showing an operation of the a liquidcrystal element as an optical coupling efficiency element shown in FIG.9.

FIGS. 11A and 11B are schematic views showing a third embodiment of thesecond implementation system of the optical coupling efficiency varyingelement of the optical head.

FIGS. 12A and 12B are schematic views showing a fourth embodiment of thesecond implementation system of the optical coupling efficiency varyingdevice of the optical head.

FIGS. 13A to 13D depict timing charts for illustrating the state of thelaser light accompanying the recording mode/reproducing mode switchingoperations in the optical recording medium driving device.

FIG. 14 is a flowchart for illustrating an operation of holding the“attenuate” state, which so far prevailed, in the “standby” state, andfor “switching the attenuate state” subsequent to receipt of a commandfor “recording” in the optical recording medium driving device.

FIG. 15 is a flowchart for illustrating an operation of holding the“attenuate” state, which so far prevailed, in the “standby” state, andfor “switching the attenuate state” subsequent to receipt of a commandfor “reproduction” in the optical recording medium driving device.

FIG. 16 is a flowchart for illustrating an operation of setting the“attenuate” state, with low optical coupling efficiency, which so farprevailed, in the “standby” state, at all times, and for switching tothe “attenuate” state, with high optical coupling efficiency, only onreceipt of the command for “recording”, specifically, the operation onreceipt of the command for “recording” in the optical recording mediumdriving device.

FIG. 17 is a flowchart for illustrating an operation of setting the“attenuate” state, with low optical coupling efficiency, which so farprevailed, in the “standby” state, at all times, and for switching tothe “attenuate” state, with high optical coupling efficiency, only onreceipt of the command for “recording”, specifically, the operation onreceipt of the command for “reproduction” in the optical recordingmedium driving device.

FIG. 18 is a flowchart for illustrating an operation of setting the“attenuate” state, with high optical coupling efficiency, which so farprevailed, in the “standby” state, at all times, and for switching tothe “attenuate” state, with high optical coupling efficiency, only onreceipt of the command for “reproduction”, specifically, the operationon receipt of the command for “recording” in the optical recordingmedium driving device.

FIG. 19 is a flowchart for illustrating an operation of setting the“attenuate” state, with high optical coupling efficiency, which so farprevailed, in the “standby” state, at all times, and for switching tothe “attenuate” state, with high optical coupling efficiency, only onreceipt of the command for “reproduction”, specifically, the operationon receipt of the command for “reproduction” in the optical recordingmedium driving device.

FIG. 20 is a flowchart for illustrating the operation of switching tothe “attenuate” state in case of coping with plural sorts of the opticalrecording medium in the optical recording medium driving device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, preferred embodiments of an optical recordingmedium driving device of the present invention will be explained indetail. Meanwhile, the embodiments of the present invention, nowexplained, represent preferred specified embodiments of the presentinvention and hence are technically minutely defined as to details.However, the scope of the present invention is not limited to theseparticular details unless contrary statements are made in the followingdescription.

FIG. 1 is a block diagram showing a structure of an optical recordingmedium driving device 101 according to the present invention. In thisfigure, the optical recording medium driving device includes a spindlemotor 103, as driving means, for rotationally driving an optical disc102, as an optical recording medium, an optical head 104 and a feedmotor 105 as driving means for the optical head.

The spindle motor 103 is driving-controlled by a system controller 107,as disc type discriminating means, as later explained, and by a servocontrolling circuit 109, and is run in rotation at a predetermined rpm.

The optical disc 102 may be any one of a variety of optical discs, asrecording and/or reproducing discs, employing optical modulationrecording, such as so-called CD-R/RW, DVD-RAM, DVD-R/RW or DVD+RW, orany one of a variety of magneto-optical recording media.

The optical disc 102 used may be selected from at least two sorts of theoptical discs having different values of the optimum recording opticalpower and/or reproducing optical power on a recording surface, anoptical disc the recording surface of which is split into at least tworecording regions having different values of the optimum recordingoptical power and/or reproducing optical power, or an optical discincluding plural recording surfaces (recording layers) superposedtogether via a transparent substrate.

The difference in the values of the optimum recording optical power onthe recording surface may be that ascribable to difference in thevelocity with which the optical disc is run in rotation (linear velocityrelative to the optical head), that is a n-tuple speed disc compared tothe standard speed disc, in addition to that ascribable to difference inno other than the recording system of the optical disc.

The optical disc 102 used may be a multi-layered optical disc, that isan optical disc having at least two recording surfaces with the same ordifferent values of the optimum recording and/or reproducing opticalpower. In this case, difference in the optimum recording and/orreproducing optical power from one recording surface to another isproduced, depending on the manner of designing the multi-layered opticaldisc.

The wavelength of the recording and/or reproducing light of the opticaldisc used may be on the order of 400 nm to 780 nm.

The optical head 104 emits a light beam on a recording surface of theoptical disc 102 to detect the light reflected by the recording surface.The optical head 104 detects a variety of light beams, as laterexplained, based on the reflected light from the recording surface ofthe optical disc 102, to send the signals derived from the respectivelight beams to a preamplifier 120.

An output of the preamplifier 120 is routed to a signal modem/ECC block108. This signal modem/ECC block 108 modulates/demodulates signals,while appending an ECC (error correction code). The optical head 104emits light on the recording surface of the rotating optical disc 102,under a command from the signal modem/ECC block 108. By this lightemission, signals are recorded and/or reproduced on or from the opticaldisc 102.

The preamplifier 120 is configured for generating focussing errorsignals, tracking error signals and RF signals etc based on the signalsderived from the respective light beams. These signals are processed ina predetermined manner, such as demodulation and error correction, bythe servo controlling circuit 109 and by the signal modem/ECC block 108,depending on the sorts of the optical recording medium to be recordedand/or reproduced.

The so demodulated recorded signals are sent to e.g., an externalcomputer 130, via an interface 111, in case the optical disc 102 is forcomputer data storage. The external computer 130 is able to receivesignals, recorded on the optical disc 102, as replay signals.

When the optical disc 102 is for audio/visual, the signals are convertedby a D/A converter of a D/A-A/D converter 112 and the so-convertedsignals are sent to an audio/visual processor 113. The signals sent tothe audio/visual processor 113 are thereby subjected to audio/visualsignal processing and transmitted to an external imaging projectingequipment through an audio/visual signal input/output unit 114.

The optical head 104 is moved through a feed motor 105 to a presetrecording track on the optical disc 102. The servo controlling circuit109 is responsible for control of the spindle motor 103, control of thefeed motor 105, and driving control in the focussing and trackingdirections of the biaxial actuator holding the objective lens of theoptical head 104.

The servo controlling circuit 109 actuates an optical couplingefficiency varying element, provided in the optical head 104 of thepresent invention, and controls the optical coupling efficiency in theoptical head 104, that is the ratio of the light volume condensed on theoptical disc 102 to the total light volume of the light beam radiatedfrom the laser light source, so that the optical coupling efficiency forthe recording mode will differ from that in the reproducing mode.

A laser controller 121 controls the laser light source in the opticalhead 104. In particular, in the present embodiment, the laser controller121 performs the operation of differentiating the output power of thelaser light source during the recording mode from that during thereproducing mode.

Moreover, if the optical disc 102 is such a one selectively used from atleast two optical discs having different values of the optimum recordingand/or reproducing power on a recording surface, a disc sortdiscriminating sensor 115 discriminates the sort of the loaded opticaldisc 102. The case in which optical disc 102 is such a one selectivelyused from at least two optical discs having different values of theoptimum recording and/or reproducing power on a recording surfaceencompasses such cases in which the optical disc is selected from discshaving different recording formats, the optical disc selected is a discportion, in the form of one of plural split recording areas or one ofplural laminated layers, and in which the optical disc is selected fromdiscs having differential relative linear velocities with respect to thelight beam. The optical disc 102 may be one of a variety of types of theoptical discs employing optical modulation recording or one of a varietyof magneto-optical recording media, these including different values ofoptimum recording and/or reproducing power on the recording surface. Thedisc sort discriminating sensor 115 detects the difference in surfacereflectance or other difference in shape or appearance of the opticaldisc.

The system controller 107 discriminates the type of the optical disc 102based on the result of detection as supplied from the disc sortdiscriminating sensor 115.

For discriminating the sort of a disc accommodated in a cartridge, itmay be contemplated to provide a cartridge detection opening. It mayalso be contemplated to detect the “disc type” or the “recommendedrecording power or recommended reproducing power” based on pre-masteredpits on the innermost rim or based on the information in the form of thetable-of-contents (TOC) to set the recording and/or reproducing opticalpower suited to recording and/or reproduction of the optical recordingmedium.

The servo controlling circuit 109, operating as the optical couplingefficiency controlling means, controls the optical coupling efficiencyin the optical head 104, depending on the sort of the loaded opticaldisc 104, responsive to the results of discrimination of the disc sortdiscriminating sensor 115, under control by the system controller 107.

When the optical disc 102 used is the optical disc the recording surfaceof which is divided into at least two recording areas having differentvalues of the optimum recording and/or reproducing power, the recordingarea to be recorded and/or reproduced is detected, using recording areadiscriminating means. When the plural recording areas are split intoplural concentric ring-like areas having different distances from thecenter of the optical disc 102, the servo controlling circuit 109 may beused as recording area discriminating means. For example, the servocontrolling circuit 109 detects the position of the optical head 104 todiscriminate the recording area to be recorded and/or reproduced. Theservo controlling circuit 109 controls the optical coupling efficiencyin the optical head 104 depending on the result of discrimination of therecording area to be recorded and/or reproduced.

If the optical disc 102 is the multi-layered optical disc having atleast two or more recording surfaces exhibiting different values of theoptimum recording and/or reproducing power, the recording surface to berecorded and/or reproduced is discriminated by the recording surfacediscriminating means, which may, for example, be the servo controllingcircuit 109. The servo controlling circuit 109 detects the position inthe focussing direction of the objective lens of the optical head 104 todetect the recording surface to be recorded and/or reproduced. The servocontrolling circuit 109 controls the optical coupling efficiency in theoptical head 104 depending on the results of discrimination of therecording surface to be recorded and/or reproduced.

Meanwhile, the information on the sort, recording area or the recordingsurface of these optical discs may be discriminated by reading out thearchival information, such as TOC, recorded on each optical disc.

FIG. 2 is a schematic view showing an optical system of an optical head.

Referring to FIG. 2, the optical head 104 includes a light source 2, anoptical coupling efficiency varying element 3, a beam splitter 4, aslight splitting means, an objective lens 5, as light condensing means,and a photosensor 6, as photodetector means. These optical componentsare mounted in isolation from one another.

In this optical head 104, the light beam radiated form the light source2 is caused to fall on the optical coupling efficiency varying element3, and the light beam transmitted through this optical couplingefficiency varying element 3 is caused to fall on the beam splitter 4.The light beam transmitted through the beam splitter 4 is condensed bythe objective lens 5 on the recording surface of the optical disc 102.

The light beam reflected by the recording surface of the optical disc102 is separated from the optical path of the light source by the beamsplitter 4 to fall on the photosensor 6. Based on a signal received andoutput by the photosensor 6, RF signals, focussing error signals andtracking error signals, for example, are generated.

In the above-described optical head 104, the light beam radiated fromthe light source 2 has its light intensity variably controlled by theoptical coupling efficiency varying element 3 after the light beam hastraversed the optical coupling efficiency varying element 3. If, in theoptical disc, recording area or in the recording surface of the samesort, the recording mode is switched to the reproducing mode, the lightfalls on the optical disc 102 at a light intensity smaller than thelight intensity of the light source 102. If conversely the reproducingmode is switched to the recording mode, the light falls on the opticaldisc 102 at a light intensity larger than the light intensity of thelight source 102.

Referring to FIG. 3, the optical head 104 includes a semiconductor laserelement 212, a collimator lens 213, a liquid crystal element 214, afirst beam splitter 215, a second beam splitter 218, a detection elementfor FAPC (Front Auto Power Control), an objective lens 220, a detectionlens 221, a multi-lens 222 and a photodetector 223, these opticalcomponents being mounted in isolation from one another.

The current driving a semiconductor laser chip, not shown, in thesemiconductor laser element 212, is sent from a laser controller 121 ofthe optical head 104. The applied voltage to the liquid crystal element214 is controlled by the servo controlling circuit 109. Meanwhile, thelaser controller 121 may be provided outside of the optical head or maybe loaded thereon.

An optical path of the optical head 104 is now briefly explained. In theoptical head 104, the light beam radiated from the semiconductor laserelement 212 is incident on the collimator lens 213 and thereby convertedto a parallel light beam which is incident on the liquid crystal element214.

The polarization state of the crystal element 214 is changed based onthe applied voltage. The light beam transmitted through the liquidcrystal element 214 is incident on the first beam splitter 215 with itspolarization state changed.

The first beam splitter 215 is configured for transmitting approximately100% of the P-polarized light, while reflecting approximately 100% ofthe S-polarized light. In the recording mode, when the phase differenceafforded by the liquid crystal element is just equal to N wavelengths, Nbeing an integer, approximately 100% of the light beam is transmittedthrough the first beam splitter 215.

In the reproducing mode, when the phase difference by the liquid crystalelement 214 is offset by one-half wavelength from the N wavelengths, thedirection of polarization is rotated 45°, such that approximately 50% ofthe light beam is transmitted through the first beam splitter 215, withthe remaining 50% of the light beam being reflected.

The light beam reflected by the first beam splitter 215 is received by abranched light volume monitoring photodetector 216. An output of thebranched light volume monitoring photodetector 216 corresponds to theproduct of the light emission output of the semiconductor laser element212 and the light branching rate in the first beam splitter 215, andapproximately corresponds to the optical coupling efficiency in theoptical head 104. Meanwhile, if the optical coupling efficiency is highor low, the volume of light incident on the branched light volumemonitoring photodetector 216 is decreased or increased, respectively. Itshould be noted that the volume of light incident on the branched lightvolume monitoring photodetector 216 is proportionate to100%—[transmission rate (%) through the optical coupling efficiencyvarying element]. An output of the branched light volume monitoringphotodetector 216 is sent to the preamplifier 120.

The light beam transmitted through the first beam splitter 215 isincident on the second beam splitter 218. The second beam splitter 218separates the light beam, radiated from the semiconductor laser element212, into light proceeding through the objective lens 220 towards therecording surface of the optical disc 102, and into light falling on theFAPC detection element 219 designed for monitoring the volume of thelight beam proceeding to the recording surface. An output of the FAPCdetection element 219 is sent to a laser controller 121 to execute theautomatic power control operation. That is, the laser controller 121controls the light emission output of the semiconductor laser element212 so that the output of the FAPC detection element 219 will be of apreset value. This control provides for a constant output of the lightbeam emitted on the recording surface of the optical disc 102. An outputvalue of the emitted light beam, during recording, made constant on therecording surface of the optical disc 102, differs from that duringreproduction, as will be explained subsequently. Moreover, this outputvalue differs with the disc sort. It is noted that the output is pulsedlight emission in the case of the optical modulation recording system.

The light beam separated by and transmitted through the beam splitter218 falls on the objective lens 220.

The objective lens 220 converges the incident light on a point on therecording surface of the optical disc. The objective lens 220 is drivenalong the focussing direction indicated by arrow F and along thetracking direction indicated by arrow T in FIG. 3.

The reflected light from the recording surface of the optical disc againfalls on the second beam splitter 218 through an objective lens 220. Inthe second beam splitter 218, the light beam is reflected and separatedin a volume corresponding to reflectance.

The reflected light, separated by this second beam splitter 218, isconverted by a detection lens 221 into converged light, which isafforded by the multi-lens 222 with astigmatic aberration for obtainingfocussing error signals by the astigmatic method. The focussing errorsignals, tracking error signals and the RF signals may be obtained basedon an output of the photodetector 223.

If, in this optical recording medium driving device, the opticalcoupling efficiency of light radiated from the light source 2 andconducted to the optical disc 102 in the recording mode is CEW (CouplingEfficiency-Write) and the optical coupling efficiency of light radiatedfrom the light source 2 and conducted to the optical disc 102 in thesignal reproducing mode is CER (Coupling Efficiency-Read), the followingrelationship:CEW>CERmay be derived. The same may be said of the case in which the opticalcoupling efficiency of light conducted to the optical disc 102 differswith the sort of the optical recording medium.

Thus, by switching control of the optical coupling efficiency in thisoptical coupling efficiency varying element 3 during recording, duringreproduction and at the time of changing the sorts of the opticalrecording medium, the level of the light beam emitted on the recordingsurface of the optical disc may be changed appreciably between that forthe recording mode and that for the reproducing mode responsive tochange in the sort of the optical recording medium, without appreciablyincreasing the output power ratio at the time of recording to that atthe time of reproduction on the side light source 2. On the other hand,the optical coupling efficiency can be variably controlled depending onthe sort of the optical disc, difference in the recording area or on therecording surface, in accordance with the optimum optical power on therecording surface in recording and/or reproduction. Depending on thestructure of the optical system, the relationship between the opticalcoupling efficiency and the optical power on the recording surface maybe reversed from time to time.

Thus, in the present optical recording medium driving apparatus, thelight of an optimum level may be emitted on the recording surface of theoptical disc for the sort, recording area or the recording surface ofthe selected optical disc, to effect recording or reproduction, thusachieving optimum recording and/or reproducing characteristics.

The operation of the optical coupling efficiency varying element 3 inthe present embodiment is now explained in detail.

If the optical coupling efficiency in case of not using the opticalcoupling efficiency varying element 3 is CE0, the ratio of lighttransmitted through the optical coupling efficiency varying element 3for signal recording is TW and that for signal reproduction is TR, thefollowing relationship:CEW(optical coupling efficiency in signal recording)=CE0×TWCER(optical coupling efficiency in signal reproduction)=CE0×TRis derived.

On the other hand, if the required volume of light collected on therecording surface at the time of signal recording is PW, that at thetime of signal reproduction is PR, an output required in the lightsource at the time of signal recording is LDW and that at the time ofsignal reproduction is LDR, the following relationship:LDW(at the time of signal recording)=PW/CEW=PW/(CE0×TW)LDR(at the time of signal reproduction)=PR/CER=PR/(CE0×TR)is derived.

The dynamic range LDW/LDR, required for outputting the light of thelight source, may be shown as follows:LDW/LDR=(PW/PR)×(TR/TW).

The case of not employing the optical coupling efficiency varyingelement 3 is similar to the case of TR=TW. That is, in the presentoptical recording medium recording apparatus, the dynamic range requiredfor outputting the light of the light source may be changed in an amountcorresponding to the ratio of the transmitted light through the opticalcoupling efficiency varying element 3.

The case of employing plural sorts of the optical recording media is nowexplained. The usable optical recording media may be enumerated by themulti-layered optical disc, high linear velocity optical recordingmedium and so forth.

It is assumed that a semiconductor laser is used as a light source, thelight output for which the laser oscillation is stable and the lasernoise becomes sufficiently small is 4 mW, with the maximum light outputrating being 60 mW.

Moreover, it is assumed that the amounts of light collected PW(A) andPR(A) on the recording surface, as required from characteristics of theoptical recording medium A (first sort of the optical disc), are asfollows:PW(A)=20 mWPR(A)=2 mWand that the amounts of light PW(B) and PR(B) collected on the recordingsurface, as required from characteristics of the optical recordingmedium B (second sort of the optical disc), are as follows:PW(B)=10 mWPR(B)=1 mW.

In this case, if the optical coupling efficiency varying element is notused, the dynamic range of the light output of the light source may berepresented by the following equation:[dynamic range of the required light output]=60 mW/4 mW=15.

The dynamic range of the required light output on the recording surfaceof the optical disc may be represented by the following equation:[dynamic range of the required lightoutput]=LDW(A)/LDR(B)=PW(A)/PR(B)=20 mW/1 mW=20.

That is, since the dynamic range of the light output of the light sourceis smaller than that of the required light output, this light source, ifleft unmodified, cannot be used for optimum recording and/orreproduction.

On the other hand, if the optical coupling efficiency varying means ofthe present invention is not used, the result is as follows:

With the ratio of the transmitted light through the optical couplingefficiency varying means is such that T1=100% and T2=50%, with T1 beingthe value for the case of recording on the optical recording medium Aand T2 being the value for the case of reproducing from the opticalrecording medium B, the dynamic range for the required light output maybe indicated as follows:

$\begin{matrix}{\begin{bmatrix}{{dynamic}\mspace{14mu}{range}\mspace{14mu}{of}\mspace{14mu}{the}} \\{{required}\mspace{14mu}{light}\mspace{14mu}{output}}\end{bmatrix} = {{LDW}\mspace{11mu}{(A)/{LDR}}\mspace{11mu}(B)}} \\{= {\left( {{PW}\mspace{11mu}{(A)/{PR}}\mspace{11mu}(B)} \right) \times \left( {T\;{2/T}\; 1} \right)}} \\{= {{\left( {20\mspace{11mu}{{mW}/1}\mspace{11mu}{mW}} \right) \times \left( {50\mspace{11mu}{\%/100}\mspace{11mu}\%} \right)} = 10.}}\end{matrix}$

Since the dynamic range for the required light output is smaller thanthat of the light output of the light source, recording of the firstsort of the optical disc A and reproduction of the second sort of theoptical disc B become possible within the dynamic range of the lightoutput of the light source.

In this case, by designing the optical system to CE0=40%, the followingrelationship:CE1[optical coupling efficiency in recording signals on the opticalrecording medium A]=CE0×T1=40%CE2[optical coupling efficiency in reproducing signals from the opticalrecording medium B]=CE0×T2=20%is derived, so that the required light output of the light source is asfollows:[during recording signals on the optical recording medium A]LDW(A)=PW(A)/CE1=20 mW/40%=50 mW[during recording signals on the optical recording medium B]LDR(B)=PW(B)/CE2=1 mW/20%=5 mW.

In this manner, recording can be made with a light output of 50 mWhaving a wide allowance in view of the maximum light output rating of 60mW, while reproduction may be made with a light output of 5 mW having asufficient allowance in view of the light output of 4 mW for which thelaser noise becomes sufficiently small.

The following holds for the signal reproduction from the opticalrecording medium A:LDR(A)=PR(A)/CE1=2 mW/40%=5 mWLDR(A)=PR(A)/CE2=2 mW/20%=10 mW.

On the other hand, the following holds for the signal reproduction fromhe optical recording medium B:LDW(B)=PW(B)/CE1=10 mW/40%=25 mWLDW(B)=PW(B)/CE2=10 mW/20%=50 mW.

In this case, any of CE1 or CE2 may be used as the optical couplingefficiency.

Meanwhile, since a predetermined switching time interval is needed forchanging the optical coupling efficiency during recording and/orreproduction, as will be explained later, it may be said to be morepractical to use CE1 for recording and reproduction for the opticalrecording medium A and to use CE2 for recording and reproduction for theoptical recording medium B.

If the “recommended recording and/or reproducing power” is pre-recordedon the optical recording medium, any recording medium loaded may behandled in the same manner.

It is assumed that the recommended recording power and the recommendedreproducing power for a certain medium are PW0 and PR0, respectively,the optical coupling efficiency for the ratio of transmitted light inthe optical coupling efficiency varying means of approximately 100% is40%, the optical coupling efficiency when the ratio of transmitted lightin the optical coupling efficiency varying means of approximately 100%is lowered is 20%, the range of estimated PW0 is 9 mW to 22.5 mW and therange of estimated PR0 is 0.9 mW to 2.25 mW.

It is then verified in which of four areas of A, B, C1 and C2 fall thecombinations of PR0 and PW0 as read out from the optical recordingmedium, and it is then determined, for each of the verified results, howthe attenuating state in the recording mode and in the reproducing mode(ratio of transmitted light in the optical coupling efficiency varyingmeans) is to be set (this point of the subject-matter of claim 14).

That is, if the dynamic range of the light source is considered, theratio of the transmitted light needs to be lowered in the opticalcoupling efficiency varying means for PR0≦1.6, while the same rationeeds to be raised for PW0≧12.

Thus, for the range A, the ratio of the transmitted light in the opticalcoupling efficiency varying means needs to be lowered for thereproducing mode, while the same ratio is nonchalant for the recordingmode, so that, if the labor in the switching operation is taken intoaccount, it is desirable to keep the ratio of the transmitted light inthe optical coupling efficiency varying means lowered at all times.

For the range B, the ratio of the transmitted light in the opticalcoupling efficiency varying means needs to be raised for the reproducingmode, while the same ratio needs to be lowered for the recording mode.Consequently, the attenuated state needs to be switched based onswitching between the recording mode and the reproducing mode.

For the range C1, the ratio of the transmitted light in the opticalcoupling efficiency varying means is nonchalant for both the recordingand reproducing modes, so that the ratio of the transmitted light in theoptical coupling efficiency varying means may be raised at all times.

For the range C2, the ratio of the transmitted light in the opticalcoupling efficiency varying means is nonchalant for the reproducingmode, while the same ratio needs to be raised for the recording mode, sothat, if the labor in the switching operation is taken into account, itis desirable to keep the ratio of the transmitted light in the opticalcoupling efficiency varying means raised at all times.

Thus, it is advisable to raise the ratio of the transmitted light in theoptical coupling efficiency varying means at all times for both theranges C1 and C2.

If a cartridge for accommodating the optical recording medium isprovided with holes for discrimination, two holes for two bits may beprovided to permit the above-mentioned processing operations to beperformed in order to discriminate the four areas.

The value of the optical coupling efficiency may be suitably set withina range which meets the dynamic range of the light source. Three of morevalues of the optical coupling efficiency may be provided, if sodesired. In this case, preparation of a light source may be facilitated.An optical head or an optical recording medium driving device, whichgives an optical head with optimum characteristics, may be realizedwithout employing special light sources.

As for the controlling sequence in coping with a multi-layered opticaldisc, having two or more recording surfaces, disc sort data (archivaldata) recorded on a disc is first reproduced, on loading the opticaldisc 102, with a reproducing power matched to a single-layer disc, theoptimum recording power of which is smaller than that of themulti-layered optical disc. If the multi-layered optical disc is adouble-layered disc, the recording and/or reproducing power and theoptical coupling efficiency matched to the double-layered disc are set.

The optical head 104 may be such a one in which the optical couplingefficiency varying means is provided between the light source and thelight separating means and in which the optical head is formed byoptical components inclusive of the light separating means, as shown inFIG. 5. That is, the present optical head 104 includes a semiconductorlaser element 212, a collimator lens 213, a variable polarized stateliquid crystal element 234, a first beam splitter 218, a second beamsplitter 224, a detection element for FAPC (Front Auto Power Control)219, an objective lens 220, a detection lens 221, a multi-lens 222 and aphotodetector 223, these optical components being mounted in isolationfrom one another.

The current for driving semiconductor laser chip, not shown, provided inthe semiconductor laser element 212, is supplied from the lasercontroller 121 of the optical head 104. The voltage applied to theliquid crystal element 214 is controlled by the servo controllingcircuit 109. Meanwhile, the laser controller 121 may be provided outsideof the optical head or may be loaded on the optical head.

The optical path of the optical head 104 is now briefly explained. Inthis optical head 104, the light beam radiated from the semiconductorlaser element 212 falls on the collimator lens 213 and is therebytransformed into a parallel light beam which then falls on a liquidcrystal element 234.

The polarized state of the liquid crystal element 234 is changed withthe applied voltage. The light beam transmitted through the liquidcrystal element 234 is incident on the first beam splitter 218 as itsstate of polarization has been changed.

The first beam splitter 218 is configured for transmitting approximately100% of the P-polarized light and for reflecting approximately 100% ofthe S-polarized light. When the phase difference afforded by the liquidcrystal element 234 is just equal to N wavelengths, N being an integer,approximately 100% of the light beam is transmitted through the firstbeam splitter 218.

On the other hand, if the phase difference by the liquid crystal element234 is offset by one-half wavelength from N wavelengths, the directionof polarization is rotated 45°, such that approximately 50% of the lightbeam is transmitted through the first beam splitter 218, with the firstbeam splitter reflecting the remaining approximately 50% of the lightbeam.

The light beam reflected by the first beam splitter 218 is incident on asecond beam splitter 224. The light reflected by the second beamsplitter 224 is received by the branched light volume monitoringphotodetector 216. An output of the branched light volume monitoringphotodetector 216 corresponds to a product of the light emission outputof the semiconductor laser element 212 and the light branching ratio inthe first beam splitter 218 and approximately corresponds to the opticalcoupling efficiency in the optical head 104. Meanwhile, if the opticalcoupling efficiency is high, the light volume incident on the branchedlight volume monitoring photodetector 216 is decreased, whereas, if theoptical coupling efficiency is low, the light volume incident on thebranched light volume monitoring photodetector 216 is increased. Thevolume of light incident on the branched light volume monitoringphotodetector 216 is proportionate to 100%—[transmission ratio (%) ofthe optical coupling efficiency varying means]. An output of thebranched light volume monitoring photodetector 216 is sent to thepreamplifier 120.

The light transmitted through the second beam splitter 224 falls on theFAPC detection element 219 operating for monitoring the light volume ofthe light beam proceeding towards the recording surface. An output ofthe FAPC detection element 219 is sent to the laser controller 121 wherethe automatic power controlling operation is executed. That is, thelaser controller 121 controls the light emission output of thesemiconductor laser element 212 so that the output of the FAPC detectionelement 219 will be of a predetermined value. This control provides fora constant output of the light beam emitted on the recording surface ofthe optical disc 102. It should be noted that a preset output value ofthe light beam emitted on the recording surface of the optical disc 102,differs in dependence upon whether the prevailing mode is the recordingmode or the reproducing mode, while also differing with the sorts of theoptical disc. Meanwhile, in case of the optical modulation recordingsystem, the light is the pulsed light.

The light beam transmitted through the first beam splitter 218 falls onthe objective lens 220. The objective lens 220 converges and emits theincident light on a point on the recording surface of the optical disc.The objective lens 220 is driven in the focussing direction, indicatedby arrow F in FIG. 3, and in the tracking direction, indicated by arrowT in FIG. 3.

The reflected light from the recording surface of the optical disc isre-incident on the first beam splitter 218 through the objective lens220. In the first beam splitter 218, an amount of the light beamassociated with reflectance is reflected and separated.

The reflected light, separated by the first beam splitter 218, istransformed by the detection lens 221 into converged light, which thenis afforded by the multi-lens 222 with astigmatic aberration usable forpreparing focussing error signals by the astigmatic aberration method.The resulting light is received by the photodetector 223. Based on theoutput of the photodetector 223, focussing error signals, tracking errorsignals and RF signals are produced.

A specified method for implementing the optical coupling efficiencyvarying element 3 is hereinafter explained.

(First Implementation System)

A first system for implementing the optical coupling efficiency varyingelement 3 in the present embodiment uses [means enabling transmittanceor reflectance of the light beam to be changed]. That is, the opticalcoupling efficiency is changed by changing the transmittance orreflectance of the light beam by these means.

(Second Implementation System)

A second system for implementing the optical coupling efficiency varyingelement 3 in the present embodiment uses [optical path branching meansfor branching the light beam into at least two optical paths]. That is,the optical coupling efficiency is changed by changing the branchingratio of two optical paths by these optical path branching means.

The respective implementation systems are hereinafter explained.

FIG. 6 schematically shows a first specified example of the firstimplementation system. The present specified example uses a transmissiontype liquid crystal element 21 as means for enabling the light beamtransmission ratio to be changed.

The present liquid crystal element 21 has its transmission ratio changedby changing the applied voltage. By changing the applied voltage, theliquid crystal of the liquid crystal element 21 is driven to control thelight transmittance. This liquid crystal element 21 is controlled byproviding a liquid crystal driving circuit in the servo controllingcircuit 109.

FIGS. 7A and 7B schematically shows a second specified example of thefirst implementation system, and uses a filter plate 22 as means forenabling the transmittance of the light beam to be changed. This filterplate 22 includes e.g., a semi-transparent filter unit 22B in a portionof a slidable transparent plate 22A.

The position of the filter unit 22B is changed on the optical path ofthe laser light to change the transmittance.

That is, by arranging the filter unit 22B on the optical path of thelaser light, as shown in FIG. 7B, it is possible to diminish thetransmitted light beam to lower the optical coupling efficiency.Alternatively, the portions of the transparent plate 22A other than thefilter unit 22B may be arranged on the optical path of the laser light,as shown in FIG. 7A, to transmit the laser light in its entirety toincrease the volume of the transmitted light to raise the opticalcoupling efficiency.

This filter plate 22 is supported by for example a piezoelectricelement. The position of the filter plate 22 is controlled bycontrolling this piezoelectric element by a driving circuit provided inthe servo controlling circuit 109. The position of the filter plate 22may also be controlled by supporting the filter plate 22 by e.g., a feedscrew or a mechanism provided to a motor and by controlling the motor bya driving circuit provided in the servo controlling circuit 109.

Although the transmission type system has been explained in the presentembodiment as the first implementation system, it is also possible toprovide a reflection type element in the optical path of the laser lightand to change its reflectance.

FIGS. 8A, 8B and 8C schematically shows a first specified example of thesecond implementation system. By providing a wavelength plate 31 and abeam splitter 32 as means for branching the light beam and byrotationally moving the wavelength plate 31 around the periphery of theoptical path, the light beam may be branched by a beam splitter film ofthe beam splitter 32.

As shown FIG. 8A, if the direction of the optical axis of the wavelengthplate 31 is coincident with the direction of polarization of theincident light, the incident light is transmitted in its entiretytowards the optical disc, without being reflected by the beam splitter32.

On the other hand, as shown in FIG. 8B, by rotating the direction of theoptical axis of the wavelength plate 31 a preset angle α from thedirection of polarization of the incident light, only a portion of theincident light may be reflected by the beam splitter 32, with only theremaining incident light being transmitted towards the optical disc.

For example, if the beam splitter film is a complete PS separating film(Tp=100% and Rs=100%), and the wavelength plate is a half wave plate,the following relationship holds for the rotational angle α and theratio of the transmitted light T:

First, if the rotational angle is α, the direction of polarization isrotated through 2α. The ratio of the P-polarized light, incident on thebeam splitter, that is the ratio of the transmitted light T, isspecified by the following relationship, as represented in FIG. 8C:T2=cos²2α=(1+cos 4α)/2.

Thus, if the optical coupling efficiency is to be 100% to 50%, switchingmay be made between α=0 deg and α=22.5 deg. This causes the direction ofpolarization to be changed by 45°, such that the ratio of thetransmitted light may be controlled to 100% or to 50%.

FIGS. 9A and 9B schematically shows a second specified example of thesecond implementation system, in which a liquid crystal element 33 and abeam splitter 34 are provided as the means for branching the light beam,and in which the liquid crystal element 33 is used as a wavelength plateto cause the light beam to be branched by a beam splitter film 34A ofthe beam splitter 34.

That is, by using the liquid crystal element 33, the rubbing directionof which is set to 22.5 deg, and by changing the phase difference fromNλ to (N+0.5)λ or from to Nλ to (N−0.5)λ, N being an integer, with λbeing a wavelength, as shown in FIG. 9A, the direction of polarizationof the incident light on the beam splitter 34 is changed by 45°, suchthat the ratio of the transmitted light may be changed within the rangeof 100% to 50%.

Moreover, by using the liquid crystal element 33, the rubbing directionof which is set to 45 deg, and by changing the phase difference from Nλto (N+0.25)λ or from to Nλ to (N−0.25)λ, N being an integer, with λbeing a wavelength, as shown in FIG. 9B the incident light on the beamsplitter 34 is changed from P-polarized light to circular polarizedlight, such that the ratio of the transmitted light may be changedwithin the range of 100% to 50%.

The principle of producing the phase difference by the liquid crystalelement is now briefly explained.

FIGS. 10A and 10B are cross-sectional views showing the cross-sectionalstructure of a liquid crystal element. Of these, FIG. 10A schematicallyshows changes in the refractive index of the liquid crystal element withrespect to the applied voltage and FIG. 10B schematically shows changesin the phase difference with respect to the applied voltage.

A liquid crystal element 40 includes liquid crystal molecules 49 sealedin-between two glass substrates 41, 42, as shown in FIGS. 10A and 10B.The liquid crystal molecules 49 are oriented by orientation films 43, 44mounted on the inner surfaces of the glass substrates 41, 42.

In-between the glass substrates 41, 42 and the orientation films 43, 44,there are mounted transparent electrode films 45, 46, respectively.

By varying the voltage applied across the transparent electrode films45, 46, the liquid crystal molecules 49 are changed from a state inwhich the liquid crystal molecules 49 are oriented parallel to theorientation films 43, 44, and along the rubbing direction indicated byarrow A, as shown in FIG. 10A, to a state in which the liquid crystalmolecules 49 are perpendicular to the orientation films 43, 44, as shownin FIG. 10B.

If the refractive index along the rubbing direction, with the liquidcrystal molecules 49 lying parallel to the orientation films 43, 44, isN1, and the refractive index along the rubbing direction, with theliquid crystal molecules 49 lying perpendicular to the orientation films43, 44, is N2, the refractive index N1 along the rubbing direction ischanged as shown in FIG. 10C, responsive to the displacement of theliquid crystal molecules 49 caused by changes in the applied voltage.Meanwhile, the refractive index in the direction perpendicular to therubbing direction N2 is constant.

As a result, the phase difference caused in the incident polarized lightin a direction along the rubbing direction is changed as shown in FIG.10D.

By exploiting this principle, the liquid crystal element may be used asa wavelength plate, such that optical path branching means can beimplemented by combining it with a beam splitter.

Meanwhile, the two examples, shown in FIG. 9, are merely illustrative,such that the range of varying the rubbing direction or the phasedifference may be set as appropriate in dependence upon the necessarychange width of the ratio of the transmitted light.

The operation of the liquid crystal element is not limited to that asthe wavelength plate, such that, for example, twisted nematic typeliquid crystal elements, used for a display, and which are able tomodify the state of polarization incident on the beam splitter, may beused with similar results.

FIGS. 11A and 11B schematically shows a third specified example of thesecond implementation system exploiting a diffraction lattice plate 35as the means for branching the light beam.

This diffraction lattice plate 35 is comprised of a slidable transparentplate 35A and a diffraction lattice portion 35B provided as a portionthereof.

The laser light branching state is changed by displacing the diffractionlattice portion 35B on the optical path of the laser light beam.

That is, by arranging the diffraction lattice portion 35B on the opticalpath of the laser light beam, as shown in FIG. 11B, the laser light maybe branched to lower the optical coupling efficiency.

By arranging the portion of the transparent plate 35A other than thediffraction lattice portion 35B, as shown in FIG. 11A, the laser lightcan be transmitted, without being branched, thereby increasing theoptical coupling efficiency.

This diffraction lattice plate 35 is carried by for example apiezoelectric element. By controlling this piezoelectric element by adriving circuit arranged on the servo controlling circuit 109, it ispossible to control the position of the diffraction lattice plate 35. Itis also possible to support the diffraction lattice plate 35 by amechanism including a feed screw or a motor and to control the motor bya driving circuit provided on the servo controlling circuit 109 tocontrol the position of the diffraction lattice plate 35.

For example, the ratio of the diffracted light volume of the diffractionlattice portion 35B is now assumed to be such that the one orderlight:zero order light:minus one order light=25%:50%:25%. For simplicitysake, ±two and higher order diffracted light is here disregarded.

In this case, the light beam used for signal recording and/orreproduction can be changed in a range from 100% to 50%. In this case,the ±one order light, not used for recording and/or reproduction can beused for other purposes, such as for canceling the crosstalk.

FIGS. 12A and 12B schematically shows a fourth specified example of thesecond implementation system. This specified example uses a liquidcrystal element 36, capable of changing the phase difference, like adiffraction lattice, as the means for branching the light beam.

This liquid crystal element 36 achieves a diffraction lattice withvariable phase depth by splitting a transparent electrode film, shownfor example in FIG. 10, into plural portions and applying differentvoltages to the respective portions, or by forming a portion of themajor surface of a glass substrate with a thickness gradient to providefor a variable thickness of the liquid crystal layer to generatelattice-like regions of differential phase difference.

With this liquid crystal element 36, the ratio of the diffracted lightvolume is varied with the phase depth (difference in the phasedifference). Thus, the liquid crystal element 36 may be used as follows:

-   [during recording] one order light:zero order light:minus one order    light=5%:90%:5%;-   [during reproduction] one order light:zero order light:minus one    order light=25%:50%:25%.

The switching operation for switching between the recording mode and thereproducing mode of the optical recording medium driving device 101 isnow explained.

FIGS. 13A, 13B, 13C and 13D shows timing charts illustrating the stateof the laser light accompanying the operation of switching between therecording mode and the reproducing mode in the optical recording mediumdriving device 101. Specifically, FIG. 13A shows the light volumecondensed on a recording surface of the optical disc 102 (disc surfacepower), FIG. 13B shows transmittance of the laser light in the opticalcoupling efficiency varying element 3, FIG. 13C shows an output of thebranched light volume monitoring photodetector 216 and FIG. 13D showschanges in the laser radiating power.

The operation of switching between the recording mode and thereproducing mode is now explained.

First, during the reproducing mode, an optimum voltage is applied by theservo controlling circuit 109 so that the phase difference will beproduced which will permit the liquid crystal element 214 to operate asa half-wave plate. The transmittance of the optical coupling efficiencyvarying element 3 is set to 50%. The laser radiating power is 5 mW, withthe laser noise being small, such that optimum reproducingcharacteristics are achieved.

In switching from the reproducing mode to the recording mode, thevoltage applied to the liquid crystal element 214 is changed by theservo controlling circuit 109, under commands by the servo controllingcircuit 109, to cause changes in the liquid crystal element 214.

In keeping with a response from the liquid crystal element 214, thetransmittance of the optical coupling efficiency varying element 3 ischanged from 50% to 100%, with the laser radiating power being changedfrom 5 mW to 2.5 mW under automatic power control.

The output of the branched light volume monitoring photodetector 216 isalso lowered at this time, responsive to changes in the transmittance ofthe optical coupling efficiency varying element 3 and in the laserradiating power.

After start of the response of the liquid crystal element 214, the lasercontroller 121 switches between the recording mode and the reproducingmode, as the timing is measured, under commands from the systemcontroller 107.

Then, in switching from the recording mode to the reproducing mode, thelaser controller 121 switches between the recording mode and thereproducing mode, under commands from the system controller 107. Thelaser radiating power is low in this state and is 2.5 mW, so that thelaser noise is in an increased state.

After the laser output is switched to the power for replay, the voltageapplied to the liquid crystal element 214 is changed by the servocontrolling circuit 109 to cause changes in the phase difference of theliquid crystal element 214.

In keeping with the response of the liquid crystal element 214, thetransmittance of the optical coupling efficiency varying element 3 ischanged from 100% to 50%. Under automatic power control, the laserradiating power is changed from 2.5 mW to 5 mW, while the laser noise isdecreased, thus allowing for detection of the optimum reproducingsignals.

An output of the branched light volume monitoring photodetector 216 isincreased responsive to changes in transmittance of the optical couplingefficiency varying element 3 and to changes in the laser radiatingpower.

If the procedure in switching the recording or reproducing mode is notcarried out as described above, the following inconveniences arise.

First, in switching from the reproducing mode to the recording mode, therecording operation is commenced while the optical output remains high,that is while the optical coupling efficiency is low. Thus, an output isto be produced which tends to exceed the maximum rating of the laseroutput light, with the consequence that the laser may be destroyed fromtime to time.

On the other hand, in switching from the recording mode to thereproducing mode, the replay operation is commenced while the opticaloutput remains low, that is while the optical coupling efficiency ishigh, such that the laser noise is significant and hence optimumreproducing characteristics cannot be achieved. Moreover, if, after therecording operation, the optical coupling efficiency is firstdiminished, an output is to be produced which tends to exceed themaximum rating of the laser output light, with the consequence that thelaser may be destroyed from time to time.

Thus, by carrying out the recording/reproducing mode switchingoperation, using the above-described procedure of the presentembodiment, the laser noise in replay can be sufficiently decreased evenwith the low laser output ratio in recording or reproduction, thusallowing to provide an optical recording medium driving device capableof achieving optimum recording and/or reproducing characteristics evenwith the use of an easy-to-produce light source with a smaller maximumrating of the light output.

Meanwhile, the optical coupling efficiency varying means may use awavelength plate type liquid crystal element, as a liquid crystalelement. This is merely illustrative such that the above-describedtiming controlling means is effective even if the optical couplingefficiency varying means of an alternative system is used.

The operation of the present optical recording medium driving device isfurther explained in detail with reference to flowcharts.

It is first contemplated to change the optical coupling efficiency inswitching between the recording and reproducing modes with use of thebranched light volume monitoring photodetector 216. As the operatingmodes of the optical recording medium driving device, three states,namely the recording mode, reproducing mode and the standby mode, may becontemplated. If the recording mode, reproducing mode and the standbymode are depicted by [W], [R] and [-], respectively, the followingchanges of the operating modes may be considered:

-   [R-W-W-R-R-R-W-R-W-R-R].

As for the timing of changing the optical coupling efficiency, that isthe timing for [switching the attenuated state], the following threetimings may be contemplated:

-   (1) In the [standby] state, the [attenuate state] which so far    prevailed is maintained, and [switching of the attenuate state] is    performed on receipt of the next command [replay] or [record] (the    operation for ths case is shown in FIGS. 14 and 15);-   (2) in the [standby] state, the [attenuate state] with low optical    coupling efficiency is always maintained, and is switched to the    [attenuate state] with high optical coupling efficiency only on    receipt of the command [record] (the operation for ths case is shown    in FIGS. 16 and 17); and-   (3) in the [standby] state, the [attenuate state] with high optical    coupling efficiency is always maintained, and is switched to the    [attenuate state] with low optical coupling efficiency only on    receipt of the command [replay] (the operation for ths case is shown    in FIGS. 18 and 19).

If, when the system controller 107 keeps the [attenuate state], which sofar prevailed, in the [standby] state, with the system controller 107then effecting the [switching of the attenuate state] on receipt of thenext [replay] or [record] command, the system controller 107 hasreceived a command [record], processing starts at step st1, as shown inFIG. 14. At the next step st2, the system controller controls thevoltage applied to the liquid crystal to verify whether the voltage hasbeen applied to the liquid crystal ([open]). If there is the voltageapplied to the liquid crystal, the system controller transfers to stepst3 and, if otherwise, to step st4. At step st4, the system controller107 controls the voltage applied to the liquid crystal to raise thevoltage applied to the liquid crystal ([open]). The system controllerthen proceeds to step st3. At this step st3, the system controller 107checks whether or not the output of the branched light volume monitoringphotodetector 216 is lower than a preset value (Poff). If the output ofthe branched light volume monitoring photodetector is lower than thepreset value (Poff), the system controller transfers to step st5 and, ifotherwise, the system controller dwells at step st3. At step st5, thesystem controller 107 checks whether or not the state in which a changewidth of the output of the branched light volume monitoringphotodetector 216 remained to be smaller than a preset value continuedfor a time interval longer than a preset width. If the state in which achange width of the output of the branched light volume monitoringphotodetector remained to be smaller than a preset value continued for atime interval longer than a preset width, the system controller 107transfers to step st6 and, if otherwise, the system controller remainsat step st5. At step st6, the system controller 107 causes the recordingoperation to be commenced. When the time is the time for terminating therecording operation, the system controller proceeds to the next step st7to terminate the recording operation. The system controller then revertsto the reproducing power to transfer to the [standby] mode. At step st8,the operation is terminated.

If, when the system controller 107 keeps the [attenuate state], which sofar prevailed, in the [standby] state, with the system controller 107then effecting the [switching of the attenuate state] on receipt of thenext [replay] or [record] command, the system controller 107 hasreceived a command [replay], processing starts at step st9, as shown inFIG. 15. At the next step st10, the system controller controls thevoltage applied to the liquid crystal to verify whether or not thevoltage applied to the liquid crystal has been lowered ([close]). If thevoltage applied to the liquid crystal has been lowered, the systemcontroller transfers to step st11 and, if otherwise, to step st12. Atstep st12, the system controller 107 controls the voltage applied to theliquid crystal to lower the voltage applied to the liquid crystal([close]). The system controller then proceeds to step st11. At thisstep still, the system controller 107 checks whether or not the outputof the branched light volume monitoring photodetector 216 is higher thana preset value (Pon). If the output of the branched light volumemonitoring photodetector is higher than the preset value (Pon), thesystem controller 107 transfers to step st13 and, if otherwise, thesystem controller dwells at step st11. At step st13, the systemcontroller 107 checks whether or not the state in which a change widthof the output of the branched light volume monitoring photodetector 216remained to be smaller than a preset value continued for a time intervallonger than a preset width. If the state in which a change width of theoutput of the branched light volume monitoring photodetector remained tobe smaller than a preset value continued for a time interval longer thana preset width, the system controller 107 transfers to step st14 and, ifotherwise, the system controller remains at step st13. At step st14, thesystem controller 107 causes the recording operation to be commenced.When the time is the time for terminating the recording operation, thesystem controller proceeds to the next step st15 to terminate therecording operation. The system controller then transfers to the[standby] mode. At step st16, the operation is terminated.

If, when the system controller 107 in the standby state always sets the[attenuate state] of low optical coupling efficiency and switches to the[attenuate state] with high optical coupling efficiency only on receiptof the [record] command, the system controller has received the command[record], the system controller has received the command [record], thesystem controller commences at step st17 and, at the next step, controlsthe voltage applied to the liquid crystal to raise the voltage ([open]),as shown in FIG. 16. The system controller then transfers to step s19.At this step st19, it is checked whether or not the output of thebranched light volume monitoring photodetector 216 is lower than apreset value (Poff). If the output of the branched light volumemonitoring photodetector 216 is lower than the preset value Poff, thesystem controller transfers to step st20 and, if otherwise, the systemcontroller dwells at step st19. At step st20, the system controller 107checks whether or not the state in which a change width of the output ofthe branched light volume monitoring photodetector 216 remained to besmaller than a preset value continued for a time interval longer than apreset width. If the state in which a change width of the output of thebranched light volume monitoring photodetector remained to be smallerthan the preset value continued for a time interval longer than a presetwidth, the system controller 107 transfers to step st21 and, ifotherwise, the system controller remains at step st20. At step st21, thesystem controller 107 causes the recording operation to be commenced.When the time is the time for terminating the recording operation, thesystem controller 107 transfers to the next step st22 to terminate therecording operation to revert to the reproducing power. The systemcontroller then transfers to step st23. At step st23, the systemcontroller 107 controls the voltage applied to the liquid crystal to setthe voltage applied to the liquid crystal ([close]). The systemcontroller then transfers to step st24 where the system controllertransfers to the [standby] mode. At step st25, the operation isterminated.

Moreover, if, when the system controller 107 in the [standby] statealways sets the [attenuate state] with a low optical coupling efficiencyand switches to the [attenuate state] with high optical couplingefficiency only on receipt of the [record] command, the systemcontroller has received the [replay] command, the system controllercommences at step st26. At the next step st27, the system controllerverifies whether or not the output of the branched light volumemonitoring photodetector 216 is higher than the preset value Pon. If theoutput of the branched light volume monitoring photodetector 216 ishigher than the preset value Pon, the system controller transfers tostep st28 and, if otherwise, the system controller dwells at step st27.At step st28, the system controller 107 checks whether or not the statein which a change width of the output of the branched light volumemonitoring photodetector 216 remained to be smaller than a preset valuecontinued for a time interval longer than a preset width. If the statein which a change width of the output of the branched light volumemonitoring photodetector remained to be smaller than the preset valuecontinued for a time interval longer than a preset width, the systemcontroller 107 transfers to step st29 and, if otherwise, the systemcontroller remains at step st28. At step st29, the system controller 107causes the reproducing operation to be commenced. When the time is thetime for terminating the reproducing operation, the system controller107 transfers to the next step st30 to terminate the recording operationto revert to the [standby] mode. The system controller then terminatesthe operation at step st31.

If, when the system controller 107 in the [standby] state always setsthe [attenuate state] with a high optical coupling efficiency andswitches to the [attenuate state] with low optical coupling efficiencyonly on receipt of the [replay] command, the system controller hasreceived the [record] command, the system controller commences at stepst32. At the next step st33, the system controller verifies whether ornot the output of the branched light volume monitoring photodetector 216is lower than the preset value Poff. If the output of the branched lightvolume monitoring photodetector 216 is lower than the preset value Poff,the system controller transfers to step st34 and, if otherwise, thesystem controller dwells at step st33. At step st34, the systemcontroller 107 checks whether or not the state in which a change widthof the output of the branched light volume monitoring photodetector 216remained to be smaller than a preset value continued for a time intervallonger than a preset width. If the state in which the change width ofthe output of the branched light volume monitoring photodetectorremained to be smaller than the preset value continued for a timeinterval longer than a preset width, the system controller 107 transfersto step st35 and, if otherwise, the system controller remains at stepst34. At step st35, the system controller 107 causes the reproducingoperation to be commenced. When the time is the time for terminating thereproducing operation, the system controller 107 transfers to the nextstep st36 to terminate the recording operation to revert to the[standby] mode. The system controller then terminates the operation atstep st37.

If, when the system controller 107 in the standby state always sets the[attenuate state] of high optical coupling efficiency and switches tothe [attenuate state] with low optical coupling efficiency only onreceipt of the [replay] command, the system controller has received thecommand [replay], the system controller commences at step st38 and, atthe next step st39, controls the voltage applied to the liquid crystalto lower the voltage ([close]), as shown in FIG. 19. The systemcontroller then transfers to step st40. At this step st40, it is checkedwhether or not the output of the branched light volume monitoringphotodetector 216 is higher than the preset value (Pon). If the outputof the branched light volume monitoring photodetector is higher than thepreset value Pon, the system controller transfers step st41 and, ifotherwise, the system controller dwells at step st40. At step st41, thesystem controller 107 checks whether or not the state in which a changewidth of the output of the branched light volume monitoringphotodetector 216 remained to be smaller than a preset value continuedfor a time interval longer than a preset width. If the state in whichthe change width of the output of the branched light volume monitoringphotodetector remained to be smaller than the preset value continued fora time interval longer than a preset width, the system controller 107transfers to step st42 and, if otherwise, the system controller remainsat step st41. At step st42, the system controller 107 causes therecording operation to be commenced. When the time is the time forterminating the reproducing operation, the system controller 107transfers to the next step st43 to terminate the recording operation torevert to the reproducing power. The system controller then transfers tostep st44. At step st44, the system controller 107 controls the voltageapplied to the liquid crystal to raise the voltage applied to the liquidcrystal ([close]). The system controller then transfers to step st45where the system controller transfers to the [standby] mode. At stepst46, the operation is terminated.

For optical recording media of different types, the system controller107 commences at step st47, as shown in FIG. 20. At the next step st48,the system controller 107 controls the voltage applied to the liquidcrystal to lower the optical coupling efficiency ([close]) to set theoutput of the emitting light beam on the recording surface of theoptical disc (disc surface power) to a predetermined value, such as 0.9mW (min). The system controller then transfers to step st49, where it ischecked whether or not the output of the branched light volumemonitoring photodetector 216 is higher than a preset value (Pon (valuecorresponding to 0.9 mW)). Since the output of the branched light volumemonitoring photodetector 216 is changed with the setting of the discsurface power, the magnitude of the setting value (Pon) is setaccordingly. If the output of the branched light volume monitoringphotodetector 216 is higher than the preset value Pon, the systemcontroller 107 transfers to step st50 and, if otherwise, the systemcontroller dwells at step st49. At step st50, the system controller 107checks whether or not the state in which a change width of the output ofthe branched light volume monitoring photodetector 216 remained to besmaller than a preset value continued for a time interval longer than apreset width. If the state in which the change width of the output ofthe branched light volume monitoring photodetector remained to besmaller than the preset value continued for a time interval longer thana preset width, the system controller 107 transfers to step st51 and, ifotherwise, the system controller remains at step st50. At step st51, thesystem controller 107 commences the focusing servo operation for theoptical head (focussing ON) and then transfers to step st52. At thisstep st52, the system controller 107 shifts the optical head to theinnermost rim of the optical disc. The system controller 107 thentransfers to step st53 where the system controller 107 detects therecommended recording power PW0 and the recommended reproducing powerPR0. The system controller 107 then transfers to step st54.

At step st54, the system controller 107 checks whether or not therecommended reproducing power PR0 is smaller than a preset value, suchas 1.6 mW. If the recommended reproducing power PR0 is smaller than thepreset value, the system controller 107 transfers to step st55 and, ifotherwise, the system controller transfers to step st158. At step st55,the system controller 107 verifies whether or not the recommendedrecording power PW0 is larger than a preset value, such as, for example,12 mW. If the recommended recording power PW0 is larger than the presetvalue, the system controller transfers to step st56 and, if otherwise,the system controller transfers to step st57.

At step st56, the system controller 107 determines that the [attenuatetype] is that shown in FIG. 4A and, based on this result of check,controls the voltage applied to the liquid crystal. At step st57, thesystem controller 107 verifies the attenuate type to be that shown inFIG. 4B and, based on this result of check, controls the voltage appliedto the liquid crystal. At step st58, the system controller 107determines the [attenuate type] to be that shown in FIG. 4C (C1 or C2)and controls the voltage applied to the liquid crystal based on theresult of check.

While the invention has been described in accordance with certainpreferred embodiments thereof illustrated in the accompanying drawingsand described in the above description in detail, it should beunderstood by those ordinarily skilled in the art that the invention isnot limited to the embodiments, but other modifications, alternativeconstructions or equivalents can be implemented without departing fromthe scope and the spirit of the present invention as set forth anddefined in the appended claims.

1. An optical recording medium driving device for recording and/orreproducing signals for at least two sorts of optical recording mediahaving respective different values of the recording and/or reproducingpower, comprising: an optical head for emitting a light beam on saidoptical recording medium; an optical coupling efficiency varying deviceconfigured to vary the optical coupling efficiency which is the ratio ofthe light volume of a light beam condensed on said optical recordingmedium to the light volume of a light beam emitted by said optical head;an optical coupling efficiency controlling device configured to controlthe optical coupling efficiency varying device; said optical couplingefficiency controlling device configured to control said opticalcoupling efficiency varying device depending on the sort of the opticalrecording media; and a temporal relationship controller configured tocontrol a temporal relationship between a first timing of changing theoptical coupling efficiency and a second timing of changing the lightvolume of light condensed on a recording surface of said opticalrecording medium, wherein said optical coupling efficiency varyingdevice including an optical path branching device configured to branchan input light beam into at least two optical paths, and the ratio ofbranching of the light volume to said least two optical paths is variedto vary the optical coupling efficiency.
 2. The optical recording mediumdriving device as recited in claim 1 wherein said optical couplingefficiency varying device is formed by a liquid crystal element and abeam splitter film.
 3. The optical recording medium driving device asrecited in claim 1 wherein said optical coupling efficiency varyingdevice is formed by a liquid crystal element having an area the phasedifference of which is variably controllable like a diffraction grating.4. The optical recording medium driving device as recited in claim 1wherein said optical coupling efficiency varying device is formed by adiffraction grating and means for displacing said diffraction grating.5. An optical recording medium driving device for recording and/orreproducing signals for at least two sorts of optical recording mediahaving respective different values of the recording and/or reproducingpower, comprising: an optical head for emitting a light beam on saidoptical recording medium; an optical coupling efficiency varying deviceconfigured to vary the optical coupling efficiency which is the ratio ofthe light volume of a light beam condensed on said optical recordingmedium to the light volume of a light beam emitted by said optical head;an optical coupling efficiency controlling device configured to controlthe optical coupling efficiency varying device; said optical couplingefficiency controlling device configured to control said opticalcoupling efficiency varying device depending on the sort of the opticalrecording media; and a temporal relationship controller configured tocontrol a temporal relationship between a first timing of changing theoptical coupling efficiency and a second timing of changing the lightvolume of light condensed on a recording surface of said opticalrecording medium, wherein said optical coupling efficiency varyingdevice is formed by a wavelength plate, a rotation displacement deviceconfigured to rotationally displace said wavelength plate, and a beamsplitter film.
 6. An optical recording medium driving device forrecording and/or reproducing signals for at least two sorts of opticalrecording media having respective different values of the recordingand/or reproducing power, comprising: an optical head for emitting alight beam on said optical recording medium; an optical couplingefficiency varying device configured to vary the optical couplingefficiency which is the ratio of the light volume of a light beamcondensed on said optical recording medium to the light volume of alight beam emitted by said optical head; an optical coupling efficiencycontrolling device configured to control the optical coupling efficiencyvarying device; said optical coupling efficiency controlling deviceconfigured to control said optical coupling efficiency varying meansdepending on the sort of the optical recording media; and a temporalrelationship controller configured to control a temporal relationshipbetween a first timing of changing the optical coupling efficiency and asecond timing of changing the light volume of light condensed on arecording surface of said optical recording medium, wherein said opticalcoupling efficiency varying device is formed by a varying deviceconfigured to vary the transmittance or reflectance of said light beam,and said optical coupling efficiency varying device is formed by aliquid crystal element capable of varying the transmittance of the lightbeam.
 7. An optical recording medium driving device for recording and/orreproducing signals for at least two sorts of optical recording mediahaving respective different values of the recording and/or reproducingpower, comprising: an optical head for emitting a light beam on saidoptical recording medium; an optical coupling efficiency varying deviceconfigured to vary the optical coupling efficiency which is the ratio ofthe light volume of a light beam condensed on said optical recordingmedium to the light volume of a light beam emitted by said optical head;an optical coupling efficiency controlling device configured to controlthe optical coupling efficiency varying device; said optical couplingefficiency controlling device configured to control said opticalcoupling efficiency varying device depending on the sort of the opticalrecording media; and a temporal relationship controller configured tocontrol a temporal relationship between a first timing of changing theoptical coupling efficiency and a second timing of changing the lightvolume of light condensed on a recording surface of said opticalrecording medium, wherein said optical coupling efficiency varyingdevice configured to vary the transmittance or reflectance of said lightbeam, and said optical head includes a light source for radiating alight beam, a light condenser configured to emit the light beam fromsaid light source on a recording surface of said optical recordingmedium, a light separator for separating a light beam radiated from saidlight source to proceed towards said light condenser from the lightreflected by said optical recording medium and transmitted through saidlight condenser, and a photodetector for receiving the light separatedby said light separator and reflected from said optical recordingmedium, said optical coupling efficiency varying device including a setof optical components provided on an optical path between said lightsource and said light separator.
 8. An optical recording medium drivingdevice for recording and/or reproducing signals for at least two sortsof optical recording media having respective different values of therecording and/or reproducing power, comprising: an optical head foremitting a light beam on said optical recording medium; optical couplingefficiency varying means for varying the optical coupling efficiencywhich is the ratio of the light volume of a light beam condensed on saidoptical recording medium to the light volume of a light beam emitted bysaid optical head; optical coupling efficiency controlling means forcontrolling the optical coupling efficiency varying means for varyingthe optical coupling efficiency; said optical coupling efficiencycontrolling means controlling said optical coupling efficiency varyingmeans depending on the sort of the optical recording media; and meansfor controlling a temporal relationship between a first timing ofchanging the optical coupling efficiency and a second timing of changingthe light volume of light condensed on a recording surface of saidoptical recording medium, wherein said optical coupling efficiencyvarying means includes optical path branching means for branching aninput light beam into at least two optical paths, and the ratio ofbranching of the light volume to said least two optical paths is variedto vary the optical coupling efficiency.